Illustration of the greenhouse effect (Courtesy of the Marian Koshland Science Museum of the US National Academy of Sciences). Visible sunlight passes through the atmosphere without being absorbed. Some of the sunlight striking the earth is (1) absorbed and converted to infrared radiation (heat), which warms the surface. The surface (2) emits infrared radiation to the atmosphere, where some of it (3) is absorbed by greenhouse gases and (4) re-emitted toward the surface; some of the infrared radiation is not trapped by greenhouse gases and (5) escapes into space. Human activities that emit additional greenhouse gases to the atmosphere (6) increase the amount of infrared radiation that gets absorbed before escaping to space, thus enhancing the greenhouse effect and amplifying the warming of the earth. --- from a Fact Sheet produced by the PEW Center for Climate Change

The United Nations today issued a summary of its most comprehensive report* to-date on climate change, saying it's more sure than ever that global warming is caused by humans and warning of temperature and sea-level rises by the end of the century.

Global temperatures are likely to rise by 2 to 4.5 degrees Celsius by the end of this century relative to the last, with a ``best estimate'' of 3 degrees, the UN's Intergovernmental Panel on Climate Change said in the report. Sea-level gain over the same period may range from 18 to 59 centimeters, it said.

The report was produced by some 600 authors from 40 countries. Over 620 expert reviewers and a large number of government reviewers also participated. Representatives from 113 governments reviewed and revised the Summary line-by-line during the course of this week before adopting it and accepting the underlying report.

The last Ice Age was the result of a dip in global temperatures of around 4°C-5°Celsius, according to the report on climate change that was published by the UK government in October 2006..

A key change in the report's language from that used in 2001 showed there is more certainty that human activity is causing the warming. The report says the link is ``very likely'' or a probability of more than 90 percent, compared with the 66 to 90 percent likelihood signalled in 2001.

Global atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice cores spanning many thousands of years. The global increases in carbon dioxide concentration are due primarily to fossil fuel use and land-use change, while those of methane and nitrous oxide are primarily due to agriculture.

Carbon dioxide is the most important anthropogenic greenhouse gas. The global atmospheric concentration of carbon dioxide has increased from a pre-industrial value of about 280 ppm (parts per million) to 379 ppm in 2005. The atmospheric concentration of carbon dioxide in 2005 exceeds by far the natural range over the last 650,000 years (180 to 300 ppm) as determined from ice cores. The annual carbon dioxide concentration growth-rate was larger during the last 10 years (1995 – 2005 average: 1.9 ppm per year), than it has been since the beginning of continuous direct atmospheric measurements (1960–2005 average: 1.4 ppm per year) although there is year-to-year variability in growth rates.

The primary source of the increased atmospheric concentration of carbon dioxide since the pre-industrial period results from fossil fuel use, with land use change providing another significant but smaller contribution. Annual fossil carbon dioxide emissions4 increased from an average of 6.4 [6.0 to 6.8] 5 GtC (Gigatons of Carbon)) (23.5 [22.0 to 25.0] GtCO2) per year in the 1990s, to 7.2 [6.9 to 7.5] GtC (26.4 [25.3 to 27.5] GtCO2) per year in 2000–2005 (2004 and 2005 data are interim estimates). Carbon dioxide emissions associated with land-use change are estimated to be 1.6 [0.5 to 2.7] GtC (5.9 [1.8 to 9.9] GtCO2) per year over the 1990s, although these estimates have a large uncertainty. {2.3, 7.3}

The global atmospheric concentration of methane has increased from a pre-industrial value of about 715 ppb (parts per billion) to 1732 ppb in the early 1990s, and is 1774 ppb in 2005. The atmospheric concentration of methane in 2005 exceeds by far the natural range of the last 650,000 years (320 to 790 ppb) as determined from ice cores. Growth rates have declined since the early 1990s, consistent with total emissions (sum of anthropogenic and natural sources) being nearly constant during this period. It is very likely that the observed increase in methane concentration is due to anthropogenic activities, predominantly agriculture and fossil fuel use, but relative contributions from different source types are not well determined. {2.3, 7.4}

The global atmospheric nitrous oxide concentration increased from a pre-industrial value of about 270 ppb to 319 ppb in 2005. The growth rate has been approximately constant since 1980. More than a third of all nitrous oxide emissions are anthropogenic and are primarily due to agriculture.

*Only a summary of the Fourth Report was published today; full report to be published later

Dr Richard Wood, senior climate scientist at the UK Met Office and a co-ordinating author of the report comments: "The world faces a huge challenge in dealing with climate change. This report is a landmark in climate research and today's summary statement captures the important aspects of the issue and gives us a more confident view of what we might expect in the future."

"Great advances in climate change research have been made by the Met Office in recent years, but there are still major challenges ahead. In particular, there is a need for detailed regional information to help decision-makers in government and business plan for and adapt to potentially rapid and dramatic climate change. In order to do this we need to combine our first-class science with increasingly powerful supercomputers."

The chairman of the Met Office Robert Napier added: "The challenge is that climate change is not linear, the planet and all of us face uncertain consequences as temperatures rise. We need to make sense of this challenge — not to scare or alarm but to present with scientific validity the probabilities of what might happen. The Met Office has the ability, the reputation and the responsibility to do this."

Preliminary temperature figures for 2006, released today by the Met Office and the University of East Anglia (UEA's Climatic Research Unit), show the mean surface air temperature has continued to demonstrate a warming climate, both around the globe and especially here in the UK.

Worldwide, the provisional figures for 2006 using data from January to November, place the year as the sixth warmest year. This is on a record that stretches back to 1850 (the top 10 warmest years have all occurred in the last 12 years) and it could have been warmer but for a cool start due to La Nina.

In the UK, the year has been remarkable, with the Central England Temperature series setting a succession of records. Not only have individual months set new records, but more significantly, extended periods have also done so:

Warmest month on record set this July, with a mean temperature of 19.7 °C

Warmest ever September (16.8 °C)

Warmest ever April to October having a mean temperature of 14.6 °C

Warmest ever autumn with a mean temperature of 12.6 °C

2006 is very likely to be the warmest year in terms of CET. The joint warmest years currently are 1990 and 1999, which recorded a mean temperature of 10.63 °C and with just over two weeks to the end of the year, the current mean temperature anomaly to 12 December is equivalent to an annual temperature of 10.84 °C.

Professor Phil Jones, of UEA's Climatic Research Unit, said: "This year sees the highest average temperature recorded since the Central England Temperature series began in 1659, and the rise above the average is significantly higher than that for the two hottest years we have experienced."

Met Office climate scientist David Parker said, "2006 has been quite extraordinary in terms of the UK temperature, with several records being broken. The figures support recent research from Prof David Karoly of the University of Oklahoma and Dr Peter Stott at the Met Office which showed links between human behaviour and the warming trend".

Where does Bertie Ahern stand on climate change asks Friends of the Earth?

Friends of the Earth believes the significance of UN report on climate change science is clear. Humanity stands at the edge of climate disaster. Only immediate and sustained action to cut climate pollution can pull us back from the brink.

Commenting, Friends of the Earth Director Oisin Coghlan said:"This report is the starkest warning yet that we have no time to waste. What the science means is the minimum amount of warming possible is the maximum we can allow if we are to avoid climate chaos. Now the only question is one that future generations will ask us - 'What did you do when you heard it was humanity's last chance to avoid climate disaster'. That question rings loudest for our politicians. In Ireland our government has been tinkering while the world warms. Now it's time for leadership."

"This Government signed the Kyoto Protocol 10 years ago. This Government agreed to a 13% limit for our pollution growth. This Government says repeatedly that Kyoto is only a first step and more intense action will be needed. And yet 10 years on our emissions are still rising and this year the rise will reach twice our Kyoto commitment. Three Ministers for the Environment - Dempsey, Cullen and Roche - have all failed to convince the Government to take the issue seriously. Instead we have business as usual. The question is now one for the Taoiseach. Where do you stand on climate change, Bertie Ahern? Will you act to ensure Ireland does its fair share," Coghlan asked.

The FOE says that the European Union has agreed that for rich countries to do their fair share we will have to cut our pollution by 60-80% by 2050 and has proposed a cut of 20-30% by 2020, compared to a 1990 baseline. Meanwhile Ireland is failing to meet its Kyoto target of an increase of 13%, this year the rise in our emissions is forecast to reach twice that level. Among rich countries Ireland is the fifth most climate polluting country per person. And yet it is the world's poorest countries, who have done least to contribute to the problem are being hit first and will be hit hardest.